Lead body and method of lead body construction

ABSTRACT

In one embodiment, a neurostimulation lead, comprises: a lead body, the lead body comprising an inner insulator, an outer insulator positioned around the inner insulator, wherein the outer insulator and the inner insulator are fused together; at least one conductor that is wound between the inner insulator and the outer insulator; and at least one electrode that is electrically coupled to the at least one conductor.

RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. § 120 of, andis a continuation in part of, the following co-pending, commonlyassigned applications: U.S. patent application Ser. No. 09/821,919,filed Mar. 30, 2001, entitled “Lead Body and Method of Lead BodyConstruction;” and U.S. patent application Ser. No. 11/074,572, filedMar. 8, 2005, entitled “Method of Forming a Lead” which is acontinuation of U.S. patent application Ser. No. 09/822,728, filed Mar.30, 2001, entitled “Medical Lead and Method For Electrode Attachment”(now issued as U.S. Pat. No. 6,952,616) which is a continuation in partof U.S. patent application Ser. No. 09/670,062, filed Sep. 26, 2000,entitled “Medical Lead and Method For Medical Lead Manufacture,” all ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present application relates to medical devices and moreparticularly, to a lead body for a medical lead and a method forconstructing a lead body.

BACKGROUND

A variety of medical electrode catheters are available today for thediagnosis and treatment of various disorders of the cardiovascular andneurological systems. These electrode catheters can be used to senseelectrical activity within the body and to deliver different forms ofenergy to stimulate, ablate, cauterize or pace. Examples of medicalcatheters using electrodes include permanent and temporary cardiacpacing leads, electrophysiologic (EP) catheters, electrocautery probesand spinal stimulation catheters. Generally, for all applications, areduced diameter lead is desired to limit the negative steric effects oflead implantation. Therefore, a need exists for a reduced diameter leadto reduce the negative effects of lead implantation.

In addition, lead size can prevent access to certain tissues andstructures. In the case of neurostimulation, spinal cord stimulation mayhave a limited effectiveness for certain pain conditions. In many caseswhere spinal cord stimulation is inadequate, spinal or peripheral nervesmust be specifically stimulated to provide pain relief. However, accessto spinal and peripheral nerves is limited because of the limited spacefor lead placement within the intervertebral foranin. Therefore, withexisting technology, access to certain nerves is best accomplished usinga laminectomy procedure. In a laminectomy procedure, a portion of avertibrae's lamina is surgically removed to allow placement of anelectrode adjacent to the target nerve. The surgery frequently resultsin significant scarring and patient discomfort. Therefore, a need existsfor a method to manufacture of a reduced diameter body lead to provideimprove access for nerve stimulation.

Procedurally, spinal or peripheral nerve stimulation is more challengingthan spinal chord stimulation. The spinal and peripheral nerves branchoff of the spinal chord through the transverse foramen of the vertebrae.Spinal and peripheral nerve stimulation is necessary when a region ofthe body is affected that cannot be effectively stimulated via thespinal cord. To stimulate these nerves, a lead is inserted through theepidural space along the spinal chord and then turned laterally outwardto track the branching nerves. Tracking these nerves requires a leadhaving a significantly smaller diameter than conventional stimulationleads. Further, in deep brain stimulation, a reduced diameter lead mayprovide for less traumatic placement of electrodes as well as moreprecise electrical stimulation by allowing electrode placement directlyadjacent to remote target locations within the brain. Therefore, a needexists for the manufacture of a reduced diameter lead to improve accessin neurological applications.

In cardiac applications, a reduced diameter leads may provide access tolocations within the heart and veins that would not otherwiseaccessible. In addition, smaller leads allow more efficient valvefunction than their standard diameter counterparts when the lead passesthrough the valves in the heart. Further, smaller leads allow access tosmaller veins without compromising blood flow. Thus, a need exists for areduced diameter lead configured for cardiac pacing.

Prior methods for the manufacture of lead bodies either wound heatedconductors into insulating material and then passed the lead bodiesthrough a smoothing dye or wound conductors over an inner insulator andthen extruded an outer insulator over the conductors. These methods donot allow for the precise control of variables such as conductorpositioning and pitch during manufacture because the methods may permitthe conductors to float during manufacture. Imprecise positioning canresult in electrical contact between adjacent conductors resulting inthe particular lead body having to be discarded. Therefore, a needexists for a method that allows for more precise control and tightertolerances during manufacture. Further, these methods have a tendency todestroy outer coverings that may be present on the wires duringmanufacture. Therefore, a need also exists for a method of forming alead body that does not destroy the integrity of coverings, such as forexample insulators, during manufacture.

The present application meets the above needs and provides otherimprovements and advantages that will be recognized by those skilled inthe art upon review of the following description and drawings.

SUMMARY

A lead body in accordance with one embodiment includes an innerinsulator, an outer insulator and at least one conductor. The conductoris wound between the inner insulator and the outer insulator and theouter insulator and the inner insulator are fused together. When thelead body includes a plurality of conductors, the inner insulator may befused to the outer insulator to electrically isolate the conductors fromone another. The lead body may further include a lead body a lumenextending through the inner insulator along the longitudinal axis of thelead body. One or more insulating spacers may also be provided betweenthe inner and outer insulator to space and/or electrically insulate theconductors. The least one insulating spacers may be fused to either orboth of the inner insulator and the outer insulator.

A lead body in accordance with one embodiment may be manufactured bypositioning at least one conductor between an outer and an innerinsulator and fusing the outer and the inner insulators to one another.In one embodiment, the inner insulator is disposed about a mandrelintermediate a first end and a second end of the mandrel. The first endand the second end of the mandrel are typically exposed. A first end ofthe at least one conductor is secured to the first end of the mandrel.The at least one conductor is then spirally wound around the innerinsulating material and the second end of the conductor is secured tothe second end of the mandrel. One or more insulating spacers may beprovided and spirally wound between the conductors. An outer insulatingmaterial is then disposed around the wound conductor coextensive withthe inner insulating material. The inner and outer insulators are thenfused by heating. The fusing may be facilitated by disposing shrink-wraptubing over the outer insulating material and heating the shrink-wrap,the outer insulating material and the inner insulating material. Theheating shrinks the shrink-wrap tubing and forces the outer insulatingmaterial to contact the inner insulating material. The shrink-wrap maybe removed after the layers have been fused. The fusing may also befacilitated by disposing tubing over the outer insulating material,sealing a first end of the tubing, applying a partial vacuum to a secondend of the tubing, and heating the tubing. The vacuum draws the innerand outer insulators into contact with one another and the heating fusesthe outer insulating material to the inner insulating material. Themandrel may be removed from the lead body to form a lumen or may remainwithin the lead body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a longitudinal cross-section of an embodiment of alead body in accordance with one embodiment;

FIG. 1B illustrates a transverse cross-section of the embodiment of alead body as shown in FIG. 1A;

FIG. 2 illustrates a transverse cross-section of another embodiment of alead body in accordance with one embodiment;

FIG. 3 illustrates a transverse cross-section of yet another embodimentof a lead body in accordance with one embodiment;

FIG. 4A illustrates a perspective view of a mandrel covered with theinner insulator;

FIG. 4B illustrates a perspective view of a mandrel covered with theinner insulator having a conductor wound over the inner insulator;

FIG. 4C illustrates a partial cross-section of an embodiment prior tofusing the outer insulator to the inner insulator; and

FIG. 5 illustrates a lead body including an insulating spacer.

DETAILED DESCRIPTION

The present application provides a novel method for the manufacture oflead body and provides a novel lead body for use in a variety of medicalapplications. The application describes particular embodiments describedbelow for exemplary purposes only, those skilled in the art willunderstand how to apply the disclosed embodiments to a variety of leadbodies. Therefore, the appended claims are not intended to be limited toany specific example or embodiment described in this patent. Further, inthe drawings described below, reference numerals are generally repeatedwhere identical elements appear in more than one figure.

A lead body in accordance with one embodiment is illustrated in FIGS. 1Aand 1B. Lead body 10 includes a lumen 12, an inner insulator 14, atleast one conductor 16 and an outer insulator 18. Conductor 16 may be inthe form of a round wire, a square wire, a cable, or other elongatedform. Conductors 16 are shown as ribbon wire having a rectangularcross-section for exemplary purposes only. Further, conductors 16 may besolid wires, a drawn-filled-tube or other configuration of conductorthat will be recognized by those skilled in the art. Conductors 16 aretypically composed of stainless steel, MP35N, platinum, gold, silver,copper, vanadium or other metal. Further, conductors 16 may include aconductor insulator or other covering disposed about the individualconductors. Typically, the conductor insulator is a polymeric orsilicone based material. Conductors 16 typically extend from a first endto a second end of the lead body. Conductors 16 are typically woundabout the lumen and are insulated from the external environment by outerinsulator 18 and from the lumen by inner insulator 14. Inner insulator14 and outer insulator 18 are fused together during manufacture. Thefused inner insulator 14 and outer insulator 18 can electrically isolateindividual conductors 16 from one another. Inner insulator 16 and outerinsulator 18 may be the same or different materials. The inner insulator16 and outer insulator 18 are typically made from an insulating materialsuch as polyurethane or silicone rubber. To facilitate fusing duringmanufacture, the materials of inner insulator 16 and outer insulator 18have a similar melting point. The similarity between the melting pointsof inner insulator 16 and outer insulator 18 permits fusing of theinsulators after softening the materials using heat without asubstantial disruption in their shape from melting. The materialsselected for insulators 16 and 18 may have disparate durometers to alterthe flex characteristics for particular applications. Further, aninsulating spacer 21, shown in FIG. 5, may be wound between theindividual conductors during manufacture to further electrically isolateadjacent conductors. Insulating spacer 21 typically being formed of amaterial that will fuse to inner insulator 16 and outer layer 18 duringmanufacture.

FIG. 2 illustrates a transverse cross-section of another embodiment of alead in accordance with one embodiment. Lead body 20, as shown in FIG.2, includes a lumen 12, an inner insulator 14, at least one innerconductor 26, an intermediate insulator 17, at least one outer conductor36 and an outer insulator 18. Inner conductors 26 and outer conductors36 typically extend from a proximal end of the lead body to a distal endof the lead body and may be wound in the same or opposite directionswithin the lead body. Inner conductors 26 are typically wound aroundinner insulator 14 and are insulated from the outer conductors 36 byintermediate insulator 17. Outer insulator 18 electrically isolates theconductors from the exterior environment and inner insulator 16electrically isolates the conductors from the lumen. Inner insulator 16,intermediate insulator 17 and outer insulator 18 are fused together andfunction to electrically isolate the conductors from one another. Inaddition, lead body 10 may include an insulating spacer 20, as shown inFIG. 5, wound between either or both of inner conductors 26 and outerconductors 36. An insulating spacer 21 between inner conductors 26 canbe fused between inner insulator 16 and intermediate layer 17 toelectrically isolate adjacent conductors. An insulating spacer 21between outer conductors 36 can be fused between intermediate layer 17and outer insulator 18 to electrically isolate adjacent conductors.Additional insulating layers and additional layers of conductors may beprovided as required by particular applications to alter theflexibility, torquability and/or diameter of lead body 20. Whenproviding multiple layers of conductors only one layer of conductorsneed be conductive, the additional layers may be provided in a manner toconfer particular physical properties to the lead body, such astorqueability. The non-conductive materials which can be used mayinclude nylon, polytetrafluoroethylene (PTFE), and other non-conductivematerials that may be formed into filaments and wound.

FIG. 3 illustrates a transverse cross-section of yet another embodimentof a lead in accordance with one embodiment. Lead body 30, as shown inFIG. 3, includes a lumen 12, an inner insulator 14, at least oneconductor 16, an intermediate insulator 17, and an outer insulator 18.Conductors 16 typically extend from a first end of to a second end oflead body 30. Conductors 16 are typically wound around inner insulator14 and are insulated by intermediate insulator 17. Outer insulator 18may extend for the entire length of lead body 30 or for only a portionof the length of lead body 30. Outer insulator 18 may function to altereither or both of the flex characteristics of lead body 30 and thediameter along the length of lead body 30 as may be required in certainapplications. Inner insulator 16, intermediate insulator 17 and outerinsulator 18 are fused together during manufacture. In addition, leadbody 30 may include an insulating spacer 21, as shown in FIG. 5, woundbetween inner conductors 26. An insulating spacer 20 between conductors16 can be fused between inner insulator 16 and intermediate layer 17 toelectrically isolate adjacent conductors 16. An insulating spacer 21between outer conductors 36 can be fused between intermediate layer 17and outer insulator 18 to electrically isolate adjacent conductors.Additional insulating layers may be provided as required by particularapplications to alter the flexibility, torquability and/or diameter oflead body 30.

A lead body in accordance with one embodiment may be manufactured usinga process outlined in FIGS. 4A to 4C. FIG. 4A illustrates an innerinsulator 14 is disposed about a mandrel 42. Inner insulator 16 may beextruded over the mandrel or may otherwise be deposited about themandrel as will be recognized by those skilled in the art. Formanufacture of reduced diameter leads, mandrel 42 may, for example, be awire having a diameter of around 0.013 inch. Typically, the mandrel'sdiameter is selected as appropriate for the end use of the particularlead body. Further, mandrel 42 may have a variety of cross-sectionalshapes as required by particular applications. FIG. 4A furtherillustrates a pair of attachment regions 44 provided along mandrel 42.Attachment regions 44 provide locations for attachment of conductors 16,shown in FIG. 4B, during manufacture. Attachment regions 44 aretypically exposed portions of mandrel 42 without any inner insulator 14and are typically provided at both a first end 46 and a second end 48 ofmandrel 42. Typically, a length of mandrel 42 and inner insulator 14 arecut from a spool of insulator covered mandrel after a continuousextrusion process prior to forming attachment region 44, although theinsulator covered mandrel may be constructed in any of a variety ofmethods that will be recognized by those skilled in the art. The lengthof mandrel 42 and inner insulator 14 cut from the spool will depend onthe particular application for the lead body. Alternatively, mandrel 42and inner insulator 14 may be prefabricated in the desired length.Typically, attachment region 44 is formed by stripping the insulator 16from mandrel 42 after extrusion, although attachment region 44 may beformed during the deposition of inner insulator 14 on mandrel 42.Attachment region 44 provides a region of reduced diameter to which thefirst and second ends of conductors 16 will be attached to preventunwinding during manufacture. FIG. 4C illustrates the attachment of theconductors. A first end of conductors 16 is secured to an attachmentregion 44 at first end 46 of mandrel 42. Conductors 16 may be secured bywinding around attachment region 44, by adhesives, by shrink tubing, bywelding or by other methods that will be recognized by those skilled inthe art. FIGS. 4B and 4C illustrate conductors 16 secured by winding forexemplary purposes. The method of securing is typically chosen so thatthe outside diameter of the secured conductor ends does not exceed theoutside diameter of conductors 16 wound over insulator 14. Maintainingan equal or smaller diameter for the secured ends of conductors 16permits the passing of a length of outer insulator 18 in the form of atube over attachment region 44 for positioning over wound conductors 16and inner insulator 14 as illustrated in FIG. 4C. Again referring toFIG. 4B, once the proximal end of the conductor are secured, a desirednumber of conductors 16 are wound over inner insulator 14 at a desiredpitch and tension. Once the winding has reached second end 48 of mandrel42, a second end of conductors 16 is secured to a second attachmentregion 44 at second end 48 to prevent conductors from unwinding duringsubsequent steps of manufacture. In addition to conductors 16, aninsulating spacer 21, shown in FIG. 5, may be separately orsimultaneously wound between conductors. Insulating spacer 21 canfunction to maintain the spacing of the wires during manufacture and tofurther insulate the individual conductors in the finished lead body.Outer insulator 18 is then applied over conductors 16. Typically, outerinsulator 18 is provided in the form of a tube, although the materialmay be provided as a sheet and wrapped around the conductors. Additionallayers of conductors and insulators may also be provided as outlinedabove. Once outer insulator 18 has been provided over conductors 16,outer insulator 18 is fused to inner insulator 14 by heating the leadbody or alternatively, outer insulator 18 is fused to non-conductivespacer 20 and non-conductive spacer 20 is fused to inner insulator 14 byheating the lead body. Fusing requires the heating of the variousinsulating layers to a point where contact between the layers willadhere the adjacent layers. To fuse the materials, a shrink-wrap, avacuum or other method may be utilized. Using the shrink-wrap method, ashrink-wrap material is disposed about the outermost layer of insulatingmaterial. The entire assembly is then heated to shrink the shrink-wrapand soften the insulating material sufficiently to facilitate fusing ofthe inner insulating material with the outer insulating material oralternatively between the insulator layers and the non-conductivespacer. After heating, the assembly is typically allowed to cool beforeremoval of the shrink-wrap material and removal of the mandrel. Usingthe vacuum method, a tube is disposed about the outermost layer ofinsulating material. With one end of the tube sealed and the other endof the tube attached to a vacuum pump, a partial vacuum is applied andthe entire assembly is heated to soften the insulating material tofacilitate fusing. After heating, the assembly is typically allowed tocool before removal of the tubing and removal of the mandrel.

After the formation of the lead body is performed, one or severalelectrodes are formed on the distal end of the lead body to enable theassembly to be used in a neurostimulation system. Various electrodeattachment and/or formation techniques can be employed. One example of apreferred technique is disclosed in greater detail in U.S. patentapplication Ser. No. 11/074,572, filed Mar. 8, 2005, entitled “Method ofForming a Lead”. As discussed in the '572 patent application, a weldingregion is formed in a lead body by exposing a respective conductorwithin the lead body, preferably using an excimer laser, withoutbreaching an inner lumen (if present). The welding region may be in theform of a groove in the insulator. In alternative embodiments, thewelding region may take a variety of forms and orientations that exposea sufficient surface area of the respective conductor to form anelectrical connection with a conductive pad. When in the form of agroove, the welding region is typically formed such that the groove runsparallel to conductor (typically obliquely relatively to the lead bodyfor helically wound conductors).

A conductive pad is then positioned within the welding region duringmanufacture to facilitate the electrical connection of a band electrodeand the respective conductor. The conductive pad may be formed bycentering a length of wire or other piece of material over the weldingregion and melting the wire or material at a point over the weldingregion. As the material melts, the ends of the wire are drawn into thewelding region to form the conductive pad. A weld is typically used tosecure the conductive pad in electrical contact with conductor.Alternatively, the conductive pad may be secured using an adhesive. Theconductive pad may be composed of any of a variety of conductivematerials that can be welded or secured with adhesives. Some suitablemetals include stainless steel, MP35N, Pt—Ir, platinum, silver, gold,copper, vanadium or other metal that will be recognized by one skilledin the art upon review of this disclosure. The conductive pad ispositioned within the welding region so that the conductive pad is inelectrical contact with the conductor. Typically, the conductive pad iswelded to the conductor prior to placing the band electrode over thewelding regions and the conductive pad. A pulsedNeodymium:yttrium-arsenic-garnet (YAG) laser may be used to weld theconductive pad to the respective conductor.

A band electrode is placed over the lead body and welded to therespective conductive pad, thereby securing the band electrode to thelead body and electrically connecting the respective conductor and theband electrode. The band electrode may be further secured to the leadbody by swaging, crimping and/or adhesives. Alternatively, the bandelectrode may be secured to the lead body by heating the lead body.Heating the lead body stress-relieves the plastic increasing the outsidediameter and securing the band electrode over the lead body. Inaddition, heating the lead body may be used to create a lead having auniform diameter between the band electrode and the lead body.

In some embodiments, electrical contacts can be formed on the proximalend of the lead body and coupled to conductors within the lead body insubstantially the same manner as forming electrodes on the distal end(although a different technique could be used if desired). Theelectrical contacts facilitate electrical connection of the lead body toa pulse generator device (e.g., a neurostimulator). In alternativeembodiments, the electrical contacts need not be formed. Instead, thelead body is used to connect to an “extension” lead which, in turn, isconnected to the pulse generator device.

1. A neurostimulation lead, comprising: a lead body, the lead bodycomprising an inner insulator, an outer insulator positioned around theinner insulator, wherein the outer insulator and the inner insulator arefused together; at least one conductor that is wound between the innerinsulator and the outer insulator; and at least one electrode that iselectrically coupled to the at least one conductor.
 2. Aneurostimulation lead, as in claim 1, further comprising: a lumen.
 3. Aneurostimulation lead, as in claim 1, comprising: a plurality ofconductors, wherein the inner insulator is fused to the outer insulatorto electrically isolate the plurality of conductors.
 4. Aneurostimulation lead, as in claim 3, further comprising: at least oneinsulating spacer spirally wound about the inner insulator betweenrespective wound conductors to electrically isolate the wound conductorsfrom each other.
 5. A neurostimulation lead, as in claim 4, wherein theat least one insulating spacer is fused to at least one of the innerinsulator and the outer insulator.
 6. A neurostimulation lead, as inclaim 1, wherein the inner insulator and the outer insulator comprise amaterial selected from the group consisting of polyurethane and siliconerubber.
 7. A method for manufacturing a neurostimulation lead,comprising: providing a mandrel having an inner insulating materialdisposed intermediate a first end and a second end of the mandrel,wherein the mandrel extends beyond the inner insulating material at thefirst end and the second end of the mandrel; securing a first end of atleast one conductor to the first end of the mandrel; positioning the atleast one conductor spirally around the inner insulating material andsecuring a second end of the at least one conductor to the second end ofthe mandrel; disposing an outer insulating material around the woundconductors coextensive with the inner insulating material; fusing theinner insulating material to the outer insulating material to form alead assembly; forming a lead body from the lead assembly; and formingat least one electrode on a distal end of the lead body.
 8. A method, asin claim 7, wherein fusing the inner insulator to the outer insulatorfurther comprises: disposing shrink-wrap tubing over the outerinsulating material; and heating the shrink-wrap, the outer insulatingmaterial and the inner insulating material to shrink the shrink-wraptubing and fuse the outer insulating material to the inner insulatingmaterial.
 9. A method, as in claim 7, wherein fusing the inner insulatorto the outer insulator further comprises: disposing tubing over theouter insulating material; sealing a first end of the tubing; applying apartial vacuum to a second end of the tubing; and heating the tubing,wherein the partial vacuum draws the outer insulating material and theinner insulating material into contact and the heating fuses the outerinsulating material to the inner insulating material therebyencapsulating the at least one conductor.
 10. A method, as in claim 7,further comprising: removing the mandrel from the inner insulator toform a lumen.
 11. A method, as in claim 7, further comprising: removingthe shrink-wrap material.
 12. A method, as in claim 7, wherein thewinding of the conductors comprises spirally winding the conductors. 13.A method, as in claim 12, further comprising: providing at least oneinsulating spacer; and spirally winding the insulating spacer between aplurality conductors to electrically isolate each one of plurality ofconductors from one another.
 14. A method, as in claim 7, wherein theinner insulating material and the outer insulating material comprisematerial selected from the group consisting of polyurethane and siliconerubber.
 15. A neurostimulation system, comprising: a pulse generator forgenerating electrical pulses; and a neurostimulation lead for deliveringelectrical pulses from the pulse generator to tissue of the patient, theneuromodulation lead comprising: (i) a lead body, the lead bodycomprising an inner insulator, an outer insulator positioned around theinner insulator, wherein the outer insulator and the inner insulator arefused together; (ii) at least one conductor that is wound between theinner insulator and the outer insulator; and (iii) at least oneelectrode that is electrically coupled to the at least one conductor.16. A neuromodulation system of claim 15 wherein the neurostimulationlead further comprises a lumen.
 17. A neuromodulation system of claim 15wherein the neurostimulation lead further comprises: a plurality ofconductors, wherein the inner insulator is fused to the outer insulatorto electrically isolate the plurality of conductors.
 18. Aneuromodulation system of claim 17 wherein the neurostimulation leadfurther comprises: at least one insulating spacer spirally wound aboutthe inner insulator between respective wound conductors to electricallyisolate the wound conductors from each other.
 19. A neuromodulationsystem of claim 18, wherein the at least one insulating spacer is fusedto at least one of the inner insulator and the outer insulator.
 20. Aneuromodulation system of claim 15, wherein the inner insulator and theouter insulator comprise material selected from the group consisting ofpolyurethane and silicone rubber.